1. Field of the Invention
The present invention relates to a pressure control valve for a direct-injection fuel system of an internal combustion engine, having a valve housing, at least one inlet, at least one outlet, and at least one prestressed, electrically actuatable, and at least regionally spherical valve member, which cooperates with a valve seat structurally connected to the housing.
2. Description of the Prior Art
One pressure control valve of the type which the invention is concerned is known from European Patent Disclosure EP 0 267 162. In this known pressure control valve, a valve ball is seated on the end of an inlet conduit that accordingly forms a valve seat. The ball is pressed against this valve seat by a valve tappet that is acted upon by a spring. Fastened to the end of the valve tappet remote from the ball is a magnet armature, which is surrounded by an annular electromagnet. When the magnet coil is not excited, the contact-pressure force of the valve ball is effected solely by the force of the spring. Upon an excitation of the magnet coil, the magnetic force is superimposed on this. The superposition takes place in the direction of the spring force, so that depending on the intensity of the magnetic force, the closing pressure of the valve can be increased beyond what the spring alone can exert.
However, in the known pressure control valve it has been found that the quality of the pressure control does not always meet the demands made of it. In particular, it has been demonstrated that the known pressure control valve tends to high-frequency fluttering under some circumstances.
It is therefore an object of the present invention to refine a pressure control valve of the type defined at the outset such that in a simple way, it can be operated reliably and makes stable pressure control possible.
In a pressure control valve of the type defined at the outset, this object is attained in that the valve seat widens conically toward the valve member, and the ball diameter of the valve member is selected such that with the valve closed, the valve member touches the valve seat in the vicinity of the further end of the valve seat.
According to the invention, it has been recognized that the flow downstream of the point of passage between the valve seat and the valve member can be calmed or stabilized if the flow is carried radially outward through a conical widening of the valve seat. This additionally requires, however, that the narrowest point of the passageway gap between the valve member and the valve seat be located as close as possible to the farther, that is, the downstream, end of the valve seat. In such an embodiment of the valve seat and the valve member, a relatively calm, stable, radially outward-oriented flow downstream of the point of passage through the valve gap is obtained when the valve is open.
This in turn makes markedly improved quality of the open- or closed-loop control of the fuel pressure in a fuel system possible. This makes more-accurate metering of the fuel upon injection, for instance into a combustion chamber of the engine, possible, which in turn improves the fuel consumption and emissions properties of the engine. The improvement in the open- and closed-loop control quality is achieved without requiring additional components or complex machining steps. Thus the pressure control valve of the invention can be produced relatively inexpensively.
In a first refinement of the invention it is proposed that the prestressing force is adjustable, in particular by means of a spring that can be tensed by a screw. In this way, the mechanical opening pressure for each pressure control valve can be adjusted in an especially simple way.
It is also possible that the valve member is embodied as a ball, and a retaining element is provided, in which the ball is retained transversely to the actuation direction. By means of such a retaining element, it is assured that even with the valve open, that is, when the valve member is lifted from the valve seat, the annular gap between the valve member and the valve seat is approximately the same size throughout. This prevents lateral differences in pressure at the annular gap, which under circumstances could cause a lateral oscillating motion of the valve member.
It is especially preferred if the retaining element has at least three radially inward-oriented retaining tongues, each with at least one radially inner wall on which the ball rests. With such retaining tongues, an unambiguous centering of the valve member relative to the valve seat is possible, without the passage of fluid being severely impaired by the retaining element.
In an especially preferred refinement, the pressure control valve of the invention includes a valve tappet, which acts upon the valve member. In addition, at least two plastic slide bushes are provided, in which the valve tappet is retained in an axially sliding fashion. Because of such minimally frictional or even frictionless bearing support of the valve tappet, the adjustment characteristic of the valve tappet has a slight hysteresis, which contributes to fine pressure adjustment by the pressure control valve.
The triggering of the pressure control valve can be effected in an especially simple way by providing that it is actuatable electromagnetically, and at least one magnet armature is retained on the valve tappet via a compression connection.
It is also especially preferred if the pressure control valve includes a magnet core, extending coaxially to the valve tappet, on which core one of the plastic slide bushes is secured, and the plastic slide bush, toward the armature, has a shoulder which serves as a spacer between the magnet core and the armature. The shoulder assures that even with the armature attracted, a remanent air gap required for the magnetic action is always available between the magnet core and the armature. Providing a magnet core leads to a boost in the magnetic action, which improves the dynamics of the pressure control valve of the invention. Disposing the plastic slide bush on the magnet core makes a separate retaining part unnecessary, which reduces the production cost for the pressure control valve of the invention.
According to the invention, a hydraulic module can also be provided, which includes the valve housing, the inlet, the outlet, the valve member, the valve seat, the prestressing element, the valve tappet, the armature, the magnet core, and the plastic slide bushes, and a coil module can be provided, which includes at least one magnet coil, extending coaxially to the magnet armature, as well as an electrical terminal, and the hydraulic module and coil module form separate component groups from one another.
This refinement of the pressure control valve of the invention has the advantage that the hydraulic module and the coil module can be produced separately from one another, which lowers the production costs because of the different production requirements. In the case of a defect, it is possible to replace the individual modules separately. Furthermore, a separate coil module makes it possible for different coil modules, equipped with the terminals to suit customer requirements, each to be combined with the same hydraulic module. Once again, this reduces the production cost for the pressure control valve of the invention, since at least for the hydraulic module, relatively large numbers are manufactured.
Connecting the hydraulic module to the coil module is preferably done via a frictional-engagement and/or detent connection. This also creates a means of securing it for shipping, which prevents parts located on the inside from becoming soiled or damaged. The fact that the frictional-engagement and/or detent connection can be disconnected again makes easy replacement of the parts possible.
In another refinement, it is proposed that the coil module includes an approximately U-shaped bracket element, which as its base has a fastening portion with at least two laterally protruding retaining flanges and as its legs has at least two striplike encapsulation portions, which fit over the coil from outside. With the U-shaped bracket element, the pressure control valve of the invention can thus be fastened in a simple way to some element of the fuel system. At the same time, the bracket element makes a boost in the magnetic force possible, by a laterally outer encapsulation of at least one region of the magnet coil.
It is especially preferred if the bracket element, on the ends of the legs, has fastening portions, in particular detent lugs, to which a cap element can be secured, in particular calked, with which cap element the coil is magnetically encapsulated on its end. The terminal encapsulation of the coil boosts the magnetic force still further, and the retention of the applicable cap is accomplished in a simple way by the bracket element.
It is also possible that the valve housing has a laterally outward-pointing shoulder, which rests on the bracket element. In this way, there is no need for separately fastening the hydraulic module to the coil module of the built-in pressure control valve, since in the built-in position, the hydraulic module is pressed with its shoulder against the coil module by the hydraulic pressure.
To further increase the magnetic force, it is proposed that there is a gap between the valve housing and the magnet core, and the valve housing is joined to the magnet core via a ring of an antimagnetic material.
In another preferred refinement of the pressure control valve of the invention, a receiving part with a stepped bore is provided, into which bore a connection peg of the valve housing is inserted, and an inlet-side line discharges into one portion of the stepped bore while an output-side line discharges into another portion, and the inlet-side line is sealed off from the outlet-side line by a first ring seal, and the outlet-side line is sealed off from environment by a second ring seal, and the second ring seal has a larger diameter than the first ring seal, and in the built-in state, the spacing between the first ring seal and the first step of the stepped bore is less than the spacing between the second ring seal and the second step, leading to the environment, and the fastening of the valve housing to the receiving part is elastic in the axial direction. This refinement of the pressure control valve of the invention is based on the following consideration:
Should the valve member become wedged in its closing position because of a defect, this means that the pressure limiting function of the pressure control valve is no longer operative. In that case, because of the axially elastic fastening of the valve housing to the receiving part, the valve housing and as a result the entire pressure control valve can be pushed out of the receiving part or out of the stepped bore as the hydraulic pressure increases.
If the inlet and outlet and the corresponding ring seals are embodied as claimed, it is assured that whenever the connection peg moves axially out of the receiving part, first the ring seal between the inlet and the outlet slips over the corresponding step, thus establishing a direct communication between the inlet and the outlet. In this way, virtually the entire pressure control valve acts as a valve element, which with increasing hydraulic pressure is lifted from its valve seat, namely the stepped bore. Thus even if the valve member is blocked, a certain pressure limiting function of the pressure control valve is assured.